Allow templating in the SylvaUnitsReleaseTemplate

The SURT is the way a management cluster admin provides information and define available capacities

Therefore

• Templating should be allowed
• The SylvaVersion should not be allowed to be overriden
• SURT must be refered in the SWC CR (optional. If not defined, the default SURT is applied)

In order to have incremental changes, the present issue is focusing on

• Allowing templating in SURT values and valuesFrom
• Allowing empty SylvaSourceVersion

Another issue is about

• Removing SylvaSourceVersion
• Reference to a SURT